A wind turbine known in the art comprises a wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with three wind turbine blades is connected to the nacelle through a low speed shaft, as illustrated in FIG. 1.
Modern wind turbines control the load on the rotor by pitching the blades in and out of the incoming wind. The blades are pitched to optimize the power output or to protect the wind turbine from damaging overloads.
To perform the pitch, each blade is provided with a pitching arrangement comprising a pitch bearing between the hub and the blade, and, for example, a hydraulic cylinder to provide the force for pitching the blade and maintaining it in a given position.
As the size of the modern wind turbines increases, the torque needed to pitch the blades is also increased, and the simple solution to this problem would be to just increase the size of the pitch mechanism. But nowadays, the hydraulic cylinder performing the pitch operation is already so large that if it has to be increased any further it would have to be specially designed and manufactured, thereby making it very expensive.
From the Canadian patent application CA 2 667 849 A1 and the U.S. Pat. No. 4,348,155 A it is therefore known to provide each wind turbine blade with a pitch mechanism comprising more than one hydraulic cylinder to pitch each blade. The use of more than one hydraulic cylinder reduces the size of each cylinder and enable that standard off-the-shelf equipment can be used.
But these solutions entail a disadvantageous load distribution.
Therefore one aspect of the invention is to provide for an advantageous wind turbine blade pitching technique having an improved load distribution.